1. Field of the Invention
This invention relates to an image forming apparatus using an electron emitting device.
2. Relating Background Art
A thin type image forming apparatus is known which has a plurality of electron emitting devices disposed along a plane, and image forming members (which emit light, or are charged or changed in color or quality by collision of electrons, e.g., members formed of a luminescent material or a resist material) which respectively face the electron emitting devices, and on which an image is formed by irradiation with electrons beams emitted from the electron emitting devices.
FIG. 71 schematically shows an example of such an image forming apparatus, that is, a conventional electron beam display apparatus.
The electron beam display apparatus shown in FIG. 71 has a construction in which modulation electrodes are disposed between electron emitting devices and image forming members oppose each other. More specifically, this image forming apparatus has a rear plate 91, support members 92, wiring electrodes 93, electron emission sections 94, electron passage holes 95, modulation electrodes 96, a glass plate 97, a transparent electrode 98, and luminescent members 99 (image forming members 99). The glass plate 97, the transparent electrode 98 and the luminescent members 99 constitute a face plate 100. The luminescent members have luminous points 101. The electron emitting sections 94 of the electron emitting devices (constituted of components 92, 93, and 94) are formed by a thin film formation technique as a hollow structure such that the wiring electrodes do not contact the rear plate 91. The modulation electrodes 96 are disposed in a space defined above the electron emitting sections 94 (in the electron emitting direction) and therefore have the holes 95 for passage of emitted electrode beams.
In this electron beam display apparatus, a voltage is applied to each wiring electrode 93 to heat the hollow-structure electron emitting sections 94 to emit thermions from the same, voltages are applied to the modulation electrodes 96 to modulate the flow of the emitted electrons in accordance with an information signal, and the electrons are extracted through the passage holes 95 and are accelerated to collide against the luminescent members 99. The wiring electrodes 93 and the modulation electrodes 96 form an X-Y matrix to effect image display on the luminescent members 99, i.e., image forming members.
In the above-described conventional image forming apparatus, however, the image forming members (luminescent members) are disposed in the space above the electron emitting devices (in the electron emitting direction) so as to face the electron emitting devices, and the following problems are therefore encountered.
1 When each image forming member or a gas in the device (residual gas) is irradiated with an electron beam, ions (positive ions) are generated. These ions are accelerated in the direction opposite to the direction of acceleration of electrons by the high voltage for accelerating electrons. Consequently, these positive ions collide against and damage the electron emitting devices. The extent of damage thereby caused is seriously large if the device is driven under a condition that the degree of vacuum inside the device is not higher than a level at 10.sup.-5 torr. Even if high vacuum is maintained in the device, the same damage is caused during a long-time continuous operation of the device. Such damage to the electron emitting device results in a reduction in the electron emission rate (electron emission efficiency) and, in the worst case, breakdown of the device. With respect to the performance of the image forming apparatus, a reduction in the contrast of the image formed on the image forming members (luminance unevenness or luminance fluctuation of the luminescent members) is caused. PA0 2 It is difficult to strictly align the positions of the image forming members (luminescent members) and the electron emitting sections of the electron emitting devices in a horizontal direction, and a small deviation of the position results in a considerable reduction in the contrast of the formed image (luminance unevenness or a luminance fluctuation of the luminescent image). PA0 3 It is difficult to maintain a certain distance between the image forming members (luminescent members) and the electron emitting sections of the electron emitting devices, and a change in this distance (due to an impact or a thermal deformation during driving) results in an unintended reduction in the contrast of the formed image (luminance unevenness or a luminance fluctuation of the luminescent image). PA0 4 Further, by the phenomena of the problems 2 and 3, color unevenness is caused in the case of an image forming apparatus having image forming members formed of multicolor luminescent materials having colors red, green and blue, resulting in a deterioration in color reproducibility according to an information signal.